1. The Field of the Invention
The present invention relates to the support of on-line and off-line transmission and synchronization of data. More specifically, the present invention relates to systems and methods that eliminate redundant data transmission and allow multiple copies of data to be synchronized so that incremental changes made to one copy of the data can be identified, transferred, and incorporated into the other copy of the data, regardless of whether the incremental changes are made on-line or off-line.
2. The Prior State of the Art
With the advent of the personal computer as the standard information tool, individuals everywhere at anytime need access to information. Never before has there been so much information readily available or such high expectations for how much the individual will be able to accomplish by utilizing information. It is now more common than ever for multiple users to simultaneously, or in tandem, work on shared data such as, by way of example, word processing documents, electronic mail messages, spreadsheets, electronic forms, graphic images, or a host of other data objects. Thus, accessing and sharing current and accurate information among multiple users has become increasingly vital to businesses and individuals.
Traditionally, a user desiring to access shared information located on one or more servers has had to work xe2x80x9con-line.xe2x80x9d More specifically, the user logs on to a network and communicates directly with a server. All requests from the user are sent directly to the server. Prior to disconnecting the communication, the user updates the data object on the server and must request a local copy or else the user will not have access to the data object once he or she logs off the network. Once xe2x80x9coff-line,xe2x80x9d the user has no way of knowing whether the local copy of the data object contains current and accurate information because the data object on the server could have been modified by a second user while the first user was off-line. Furthermore, if the data object on the server was modified by a second user while the first user was off-line and if the first user makes changes to his/her local copy of the data object, logs on to the network, and saves the local copy on the server under the original name of the data object, changes made to the data object by the second user will be overwritten and lost.
Another limitation is highlighted when two or more users desire access to a data object simultaneously. Under the traditional method, a first user is allowed to obtain and edit the data object. Any subsequent users desiring access to the data object are limited to a xe2x80x9cread onlyxe2x80x9d access of the data object. Therefore, while the first user is using the data object, the subsequent users can access but cannot edit the data object. In order to edit, a subsequent user would be required to save the data object under a different name. Once the subsequent user completes the edits, the changes made to the data object by the first user will be overwritten and lost if the changes made by the subsequent user are saved on the server under the original name. Alternatively, if the subsequent user saves the data object on the server under a new name, multiple copies of the data object will exist on the server. One copy will contain the changes made by the first user and a second copy will contain the changes made by the subsequent user. Where multiple copies exist, it would be difficult to know which copy, if any, contains the most current and accurate information.
Using conventional techniques, clients and servers have engaged in redundant communication of information when a user has been making changes to a shared data object while the client is on-line and subsequently desires to obtain a local copy of the shared data object for use off-line. In particular, the on-line changes made to the shared data object are transmitted from the client to the server during the on-line operation of the client. When the client is about to go off-line, the client issues a request to the server for the most current copy of the shared data object in order to store the copy locally for off-line use. In response, the server transmits the current copy of the data object, which includes the changes that have recently been made by the client. In other words, the foregoing client/server communication involves changes being sent from client to server and subsequently from server to client. Such repetitive transmission of data in a network can introduce potentially significant increases in network traffic, particularly in large organizations with many clients.
It would therefore be desirable to ensure current and accurate information through a model that would synchronize all copies of a data object. It would also be desirable for a synchronization model to be able to identify which copy of a data object is more current and accurate. It would be desirable for none of the changes to be lost or overwritten when multiple copies of a data object are used to update the copy on the server. There is also a need in the art for any such synchronization model to allow multiple users to access and edit the data object simultaneously. Furthermore, it would be desirable if the synchronization mode could eliminate the creation of redundant copies of the data object. It would also be advantageous to eliminate redundant transmissions of data object between clients and servers. Any synchronization model that could exhibit such capabilities would be particularly useful if it could support changes made to local copies of data objects regardless of whether a client was on-line or off-line with the server.
The foregoing problems in the prior state of the art have been successfully overcome by the present invention, which is directed to a system and method for elimination of redundant data transmission and for incremental change synchronization between multiple copies of data. The systems and methods of the present invention allow multiple copies of data to be synchronized so that incremental changes made to one copy of the data can be identified, transferred, and incorporated into the other copy of the data. The systems and methods of the present invention produce a more efficient use of time and network bandwidth by eliminating the transmission of redundant data. Furthermore, copies of a data object can be reliably and efficiently synchronized regardless of whether the changes made to a copy of the data object are executed while the client is operating on-line or off-line.
Implementation of the present invention may take place in an environment where multiple copies of a data object or resource are present, or where a data object or resource is shared. By way of example, the present invention can be implemented in an environment where a client is connected to a server. The present invention can also be implemented in an environment where multiple clients are connected to the same server. Another example would include multiple clients connected to multiple servers. In each of the environments, the present invention preserves incremental changes to data object regardless of whether the changes are made while a client is on-line or off-line, ensures that all copies of a data object or resource are synchronized without loss of any incremental changes, and prevents the transmission of redundant data between servers and clients.
As part of the present invention, a client, while connected to a server, identifies to the server the current state of data located at the client and issues a request for the server to evaluate the state of the client""s data. The server responds to the request by returning an identification of server data that is not included in the client""s data and an identification of the client""s data that has been changed on the server. The client is then able to download from or upload to the server new or modified data.
As data is uploaded to or downloaded from the server, the data is saved in a local storage location associated with the client and remains available to the user after the client is no longer connected to the server. In other words, as a client interacts with a server, the client stores a copy of the data object or resource and corresponding identification in cache. Therefore, when the client is xe2x80x9coff-linexe2x80x9d from the server, the client is still able to work on the data object or resource as if it were xe2x80x9con-linexe2x80x9d because a copy is located in the client""s cache. Furthermore, the presence of the data object or resource copy in cache prevents the need to download a copy from a server each time that the user desires to obtain the data object or resource. Thus, the repetitive transmission of the same data between a client and server is reduced or eliminated according to the invention.
Later, when the client is again xe2x80x9con-line,xe2x80x9d all copies of the data object or resource are synchronized. The client identifies to the server the current state of the copy in the client""s cache. The server determines if the copy in the client""s cache is the most current version of the data object or resource, and all copies of the data object are synchronized to the most current version. If there are conflicts between copies of the data object or resource, the conflicts are detected and resolved and all copies are synchronized to reflect the most current version of the data object or resource.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.